1. Field of the Invention
The present invention relates generally to a battery, and, more particularly to a vehicle battery module having a plurality of flat, rectangular shaped electrochemical or electrostatic cells having flexible tabs for terminals.
2. Description of the Related Art
A secondary battery is a device having one or more electrochemical or electrostatic cells, hereafter referred to collectively as “cells”, that can be charged electrically to provide a static potential for power or released electrical charge when needed. The cell is basically comprised of at least one positive electrode and at least one negative electrode. One common form of such a cell is the well-known secondary alkaline cell packaged in a cylindrical metal can. Examples of chemistry used in such secondary cells are nickel cadmium (NiCd), nickel zinc (NiZn), and nickel metal hydride (NiMh). Other types of cells include capacitors, which can come in the form of electrolytic, tantalum, ceramic, magnetic, and include the family of super and ultra capacitors. Such cells are mass produced, driven by an ever-increasing consumer market that demands low cost rechargeable energy for portable electronics. Energy density is a measure of a cell's total available energy with respect to the cell's mass, usually measured in Watt-hours per kilogram, or Wh/kg. Power density is a measure of the cell's power delivery with respect to the cell's mass, usually measured in Watts per kilogram, or W/kg.
In order to attain the desired operating voltage level, cells are electrically connected in series to form a battery of cells, what is typically referred to as a battery. In order to attain the desired current level, cells are electrically connected in parallel. When cells are assembled into a battery, the cells are often linked together through metal strips, straps, wires, bus bars, etc., that are welded, soldered, or otherwise fastened to each cell to link them together in the desired configuration.
Secondary batteries are often used to drive traction motors in order to propel electric vehicles. Such vehicles include electric bikes, motorcycles, cars, busses, trucks, trains, and so forth. Such traction batteries are usually large format types, comprised of tens to hundreds or more individual cells. The cells are linked together internally and installed into a case to form the completed battery.
Cells come in various shapes and sizes. One example is the cylindrical metal can style, such as the familiar AA, SC, C, and D cells, among others. Such cells are physically robust and can be soldered or welded together to form large batteries. One drawback to metal can cells is the increased mass driven by the metal can itself. Another is the inability of the metal can to expand in order to accommodate gas density variations in the cell, which can occur in some chemistry types. Increased internal pressure can be hazardous as the build up can result in cell rupture or even explosion.
Another type of cell is the flat rectangular type, which is often packaged in a flexible container. These cells are lighter than their metal can counterparts, and can expand and contract in order to equalize internal pressures. These cells are also lower cost to manufacture, and are thus preferable to use in application for these reasons. Flat rectangular cell terminals typically take the form of a pair of flexible conductive tabs, one positive and one negative. These tabs are soldered or welded to bus bars and formed into larger batteries.
Flat rectangular cell terminals typically take the form of a pair of tabs, one positive and one negative. These tabs are soldered or welded to bus bars and formed into larger batteries. One drawback with these cells is that the tabs are mechanically weak and prone to breaking and tearing. In addition, welding is difficult as the thin tabs are not conducive to welding, increasing assembly time and cost. Another problem is series connection, which requires many small bus bars to join cells together in an alternating fashion to increase voltage.
Welded or soldered straps and wire interconnects also reduce cell performance through the generation of heat. The wires and straps themselves have electrical resistance that creates significant amounts of heat when a current passes through, and can get very hot under high current traction motor situations such as acceleration. This heat reduces the power and energy coming out of the battery, and, more importantly, heat is imparted directly to the cells. Heat is one of the most important contributors to reduced cell life. Some cells can see a drop by 50% or more in life cycle when operated at elevated temperatures. Cycle life is very important in vehicle applications where the battery investment may be very high.
Thus, a vehicle battery module solving the aforementioned problems is desired.